Question about PH and New Plaster

[phalcon51]

We had our pool replastered in September 2010, about 6 months ago. I've been following the BBB method since the refill and had a couple of questions. I posted before that there were what looked like cracks appearing on the steps in the shallow end and for about 10" below the tiles around the top of the pool. Here's a picture of the steps (color enhanced to bring out the appearance of the "cracks" - they're quite visible but don't photograph well):

The pool builder came out a couple of weeks ago to look at it and said that they are microscopic cracks in the surface of the plaster caused by the plaster drying before being filled up to that level. It was a hot day, over 100 degrees, when they began filling the pool in the late afternoon. Using two hoses it filled all night and finished up midmorning the next day. He said the whitish area delineating the cracks was primarily a surface effect and should go away over time. He recommended that I keep the PH at 7.2 for a while to accelerate this process and to just keep an eye on it.

Here's my question: does this sound like a reasonable thing to do? Will a PH this low cause any problems if kept there for a couple of months? Any idea what process is going on with the plaster and the acid that would remove the appearance of the cracks?

Also, I seem to be using quite a bit of acid in general. Here's a graph of my acid use thanks to Dale.s for the Excel spreadsheet:

I seem to be adding about a quart to a quart and a half every 4 or 5 days. Is this reasonable with 6 mo. old plaster?
If I try to keep it at 7.2 consistently I'll be adding acid every couple of days.

Here's the rest of my chem specs as of today:

FC 3
CC 0
PH 7.7
TA 80
CH 300
CYA 60
Borate 0
Salt 3425
Temp 63

Thanks for any help

Gary

 

[JasonLion]

If you let your TA level come down a little further and don't lower PH, the amount of acid you need to use will go down. You will probably continue to need some acid for several months yet, plaster continues to cure for quite some time, just not as much as you are using now.

Given you various levels, having PH at around 7.2 will be a very very mild no drain acid wash, which will probably help clean up the surface appearance. It will do this by removing a small amount of plaster off the surface of the plaster (everywhere). This will also raise the CH level in the water noticeably. You don't want to do too much of that, but a little (weeks, a few months) is probably alright. Bringing PH down that low will increase the rate at which the PH increases, and bring the TA steadily down. You will need to keep an eye on that, as you won't be able to stabilize things with PH that low and will need to add acid regularly and baking soda occasionally to keep things in range.

 

[phalcon51]

Thanks Jason, much appreciated.

 

[phalcon51]

A quick follow-up question: If I keep the PH at a more reasonable 7.5 - 7.8 will the same changes take place, just over a longer period of time?

Gary

 

[PoolGuyNJ]

No, in fact the desired effect will stop in most cases. A lookup of Calcium Saturation Index or Langlier Saturation Index. The two are slightly different but have similarly useful information that will help you to understand what pool plaster finishes like chemically.

Scott